This invention relates to digital packet telecommunications, and particularly to management of flow of data, that is, the volume of data per unit of time across heterogeneous network boundaries. It is particularly useful in a digitally-switched packet telecommunications environment normally not subject to data flow rate control. The present invention is intended to work in an environment having a metered-release of acknowledgements and a window control mechanism.
This invention represents an augmentation of the capabilities disclosed in the work of Robert Packer, as for example described in U.S. Pat. Nos. 6,018,516; 5,802,106; 6,038,216; 6,046,980; 6,205,120; 6,285,658; 6,298,041 and 6,115,357. The Packer packet flow rate control mechanisms taught therein controlled size of the sliding window, amount of acknowledged data and timing of acknowledgement delivery.
The ubiquitous TCP/IP protocol suite intentionally omits explicit supervision of the rate of data transport over the various media which comprise a network. While there are certain perceived advantages, this characteristic of TCP/IP has the consequence of juxtaposing very high-speed packet flows and very low-speed packet flows in potential conflict for network resources, which results in inefficiencies. Certain pathological loading conditions can result in instability, overload and data transfer stoppage. Therefore, it is desirable to provide some mechanism to optimize efficiency of data transfer while minimizing the risk of data loss. Data flow rate capacity information is a key factor for use in resource allocation decisions.
The technology of interest is based largely on the TCP/IP protocol suite, where IP, or Internet Protocol, is the network layer protocol and TCP, or Transmission Control Protocol, is the transport layer protocol. At the network level, IP provides a “datagram” delivery service. By contrast, TCP builds a transport level service over the datagram service to provide guaranteed, sequential delivery of a byte stream between two IP hosts.
Conventional TCP flow control mechanisms operate exclusively at the end stations to limit the rate at which TCP endpoints emit data. However, TCP lacks explicit data rate control. In fact, until the work of Packer, there was no concept of coordination of data rates among multiple flows.
The basic TCP flow control mechanism is a sliding window superimposed on a range of bytes beyond the last explicitly-acknowledged byte. Its sliding operation limits the amount of unacknowledged transmissible data that a TCP endpoint can emit.
The sliding window flow control mechanism works in conjunction with the Retransmit Timeout Mechanism (RTO), which is a timeout to prompt a retransmission of unacknowledged data. The timeout length is based on a running average of the Round Trip Time (RTT) for acknowledgment receipt, i.e., if an acknowledgment is not received within (typically) the smoothed RTT+4*mean deviation, then packet loss is inferred and the data pending acknowledgment is retransmitted.
Data rate flow control mechanisms which are operative end-to-end without explicit data rate control draw a strong inference of congestion from packet loss (inferred, typically, by RTO). TCP end systems, for example, will ‘back-off’, i.e., inhibit transmission in increasing multiples of the base RTT average as a reaction to consecutive packet loss.
While TCP rate control has significant advantages, there are certain conditions where the response time needed to adjust rate control mechanisms is less than can be provided by Packer packet flow rate control techniques.